In theory, Mr. Blair's commanding parliamentary majority allows him to move promptly on welfare and pension reform. It certainly affords him leverage on those two major pressures on the budgets of Europe and North America. That's leverage his supposed prototype, Bill Clinton, would envy. (Clinton governs, after all, with less than a 50 percent popular mandate and opposition control of Congress.)

And finally, in theory, Blair can lead the United Kingdom into Europe with less party opposition than John Major faced.

In theory, yes. But what about in practice?

Mr. Blair has reinvented the Labor Party. He has reinvented himself. Will he now try to reinvent Britain and its role in the world?

Let's examine this list of potentially historic changes that Britain's youngest prime minister in 185 years has hinted he might wish to leave as a legacy for what he has repeatedly called "a new age of achievement."

First, devolution, roughly parallel to the American process of "returning power to the states." The new prime minister at first talked of creating a Scottish parliament but then reconsidered and promised instead to hold a referendum among Scots to determine not only whether they want their own legislature but whether it should have the power to tax.

Presumably Wales would be given a similar opportunity to opt for its own assembly.

But if regional legislatures could add their levies to national taxes voted in the Mother of Parliaments, what would become of Labor's pledge not to raise income taxes?

Next, corporate governance. With all of Mr. Blair's pledges not to upset the business-led prosperity that has placed Britain at the forefront of Europe in job-creation and economic growth, it's unlikely he will push major changes upon British corporations - the engine of that growth.

Nor is it likely that his social democratic counterparts on the Continent would be happy if this New Labor government were to trigger a downturn by hamstringing business.

Welfare and pension reform? Bill Clinton wrestled long and anxiously before agreeing to welfare reform. He still resists even marginal shrinkage in Social Security pensions. Alter ego Tony Blair, facing pressures from his left, also will proceed with caution.

And joining Europe? Specifically using the euro as coin of the realm? Laborite opponents now are fewer and generally less fratricidal than Mr. Major's dissidents. But Mr. Blair probably couldn't clear all the hurdles in time for the first euro round, anyway.

So, politically he will be wise to push passage of promised legislation on the home front before tackling closer ties to the Continent. His pledge of toughness on youth crime is certainly doable. Presumably he can also find money in the budget, sans new income taxes, to do something about smaller pupil-teacher ratios and modest improvement in health-care waiting times.

As to another laudable pledge, job training for youths, he would do well to note the poor record of most government training programs aimed at private-sector jobs. It's usually more practical to coax businesses to establish training programs for the kind of employees they need.

Labor strategists reportedly were stunned by their huge victory margin. Two things should be said about the landslide:

First, it was welcome, in the sense that for democracy to succeed, political parties must alternate. Otherwise the "ins" become tired, often corrupt, and short on fresh ideas. "Outs" can refresh government. And they need to confront the realities of power.

Second, it must be said that landslides seldom have lasting effect. Remember how often in the past half century the death of either Labor or Tory government has been reported, only to witness a magical rebirth? The 18 years that Labor wandered in the wilderness were unusual. If the same fate now seems landed on the Tories, some skepticism is in order.

Britain has spent much of the post-World War II era "searching for a new role." First there was learning to live without an empire. Then, finding a logical trading arena: the Commonwealth, transatlantic, or Europe? The Thatcher era brought a dynamic role: setting the economic style for much of the world.

Now that world waits to see if this Labor prime minister, who confesses to admiring Mrs. Thatcher, can find yet another new role. He has rather grandly promised "a Britain united to win in the new millennium." We wish him well, particularly on the uniting.